Many institutions, such as prisons, nursing homes, mental institutions, etc., include controlled telecommunications systems that offer inmates or residents limited calling access. One reason for controlling use of the system is to prevent the institution from incurring unaccountable telephone costs. Other reasons for controlling access to the system include preventing harassing calls to outside parties, preventing fraudulent activities, etc. Therefore, systems in such environments often monitor and control the telephone activity of each inmate or resident. For example, systems may restrict calling to only certain telephone numbers. Systems may also have a means of maintaining call records for each inmate or resident, and a means for communicating with called parties to enable the called parties to prevent future telephone calls from inmates or residents. In short, the communications system used in a regulated institution must employ unique monitoring and control functions often unnecessary in other types of telecommunications systems.
In order for the methods of monitoring and control to be effective, it is important to prevent inmates or residents from exploiting any loopholes that can be used to bypass the control features of the system. For example, inmates or residents have been known to use three-way calling to have an outside party connect the inmate or resident to a blocked number. A three-way call is initiated when the remote called party depresses the hook switch on the telephone, generating a hook flash signal. The caller is temporarily put on hold while the called party establishes a connection with a third party. Then, all three parties can converse. Using three-way calling, the inmate or resident may utilize the institution's call system to, among other things, access blocked telephone numbers, for example, to perpetrate additional criminal activities, or harass certain parties.
It is therefore critical to carefully monitor all outgoing telephone calls for three-way call attempts. Without such monitoring, many of the system's control features of a telecommunications system can be rendered ineffective. Currently, there are systems and methods known in the art for detecting three-way call attempts. Many of these systems however, are inaccurate and subject to both false positives and false negatives. Also, many of these systems are effective only in certain types of telecommunications systems.
For example, one such system known in the art for detecting three-way call attempts monitors for pulses of energy indicative of a hook-flash by detecting the frequency of the energy pulse to determine if it is characteristic of a hook-flash (i.e., a three-way call attempt). Specifically, the system includes a low pass filter for passing energy signals having frequencies below 500 Hertz (“Hz”), preferably in the range of 100 to 300 Hz, and an energy detector for detecting specific electrical energy pulses passing through the filter and having a predetermined minimum magnitude. The system also includes a software window analyzer, which cooperates with the energy detector to detect specific events, such as sound, occurring on the telephone line during a predetermined time window after the detection of the aforementioned energy pulse. The software window analyzer includes a timer means that is activated by the detection of the energy pulse, and a sound means for detecting the occurrence of sound on the telephone line during at least one of multiple windows of time defined by the timer means. The non-occurrence of sound on the telephone line during a specified time window is used by the system to confirm that the detected energy pulse is in fact a three-way call attempt. A counter means is further implemented for counting specific energy pulses detected by the energy detector during the time window when the remote party is using a pulse-dial telephone. This system, by simply monitoring for a pulse composed of certain frequencies, is often inaccurate and cannot operate in digital systems.
A similar system is also designed to detect the presence of an energy pulse indicative of a hook-flash. Specifically, the system is designed to detect a pulse that is comprised of frequency components below 500 Hz and above a predetermined threshold. The existence of the hook-flash is confirmed by digital signal processing equipment which identifies a rapid drop-off in energy, which is indicative of a hook-flash signal. Optionally, the hook-flash may be further confirmed by including software for cooperating with the energy detector to ascertain whether sound has occurred in the telecommunication during a predetermined period following the first hook-flash signal.
Still another known system includes three-way call detection circuit that uses digital signal processing to identify a third party connection. The system operates by establishing a baseline background noise. The system identifies a drop in noise level below the established baseline background noise as an indication that a three-way conference call has been attempted by the called and/or calling party.
Yet another known system monitors all connected telephone lines for indicia representative of a three-way call attempt. For example, the system may monitor for a digital PCM signal or a period of silence, followed by a release pulse, followed by yet another period of silence. Upon detection of a possible three-way call attempt, the three-way call detection circuit examines the digital signals to determine the spectral characteristics (i.e., time duration, frequency, and energy level) of a suspected release pulse of the suspected three-way call attempt. The system utilizes pattern recognition techniques to compare the suspected release pulse with a reference release pulse indicative of a three-way call attempt. The system also monitors for periods of silence before and after the suspected release pulse. If the system finds that the suspected release pulse is substantially similar to the reference release pulse and that the correct periods of silence surrounding the suspected release pulse are present, the system responds to the detection, for example, by disconnecting the telephone call, playing a recording, or creating a record of the three-way call attempt.
Yet another known system for detecting three-way calls monitors audio signals for features that distinguish voice and line-generated audio signals from audio signals produced by events associated with three-way call attempts. The distinguishing features used are pulse patterns that are strongly correlated with either audio signals generated by central office switching activity (‘clicks’) (reference features) or voice-generated audio signals (reset features). Audio signals are continuously monitored for reference and reset features over selected intervals or sampling windows. Sampling windows are reset whenever reset features are detected in the associated audio signal segment. Audio signals that are free of reset features and include reference features are tagged as potential click events. A three-way call event is declared when audio signals associated with consecutive sample windows are tagged as potential three-way call events. In this system, a control program samples the audio signal at the selected rate and sorts the sampled signals during a sampling window to produce a profile of the sampled audio signal. The profile comprises counters for tracking the number, strength (loudness), and separation of signal pulses. These counters may be compared in various combinations with counter values extracted from voice-generated audio signals (reset thresholds) and three-way call generated audio signals (reference thresholds) to declare a three-way call attempt, continue sampling, or reset the sampling window.
Another known system counts signal characteristics to detect three-way call attempts. The system samples audio from a telephone conversation, sorts the sampled signals into a profile of levels for the sampled audio signals, and monitors the profile of sampled audio signals for reset and reference conditions. In this system, a reset condition is a pulse pattern inconsistent with patterns generated by three-way call events. Reference conditions, in contrast, are pulse patterns identified from sampled audio signals that are consistent with patterns generated by three-way call events. If a reference condition is detected, the telephone call is tagged as having a possible three-way call attempt. The system concludes that a three-way call attempt has occurred when two consecutive tags have been made to the same telephone call.
Still another known system detects three-way calls by recognizing that each telephone connection has a characteristic reflection, or echo, idiosyncratic to that connection. The echo characteristics of a particular telephone connection are altered, for example, when a three-way calling feature is activated by the remote party at the original destination thereby adding a third party at a secondary destination. The system includes means for “zeroing out” or canceling the characteristic echo once a connection has been established by using an adaptive finite impulse response (FIR) filter. The system also includes response means for implementing a predetermined response when an undesirable event is detected. Examples of the responses which can be pre-programmed include call termination, playing a prerecorded message, generating a tone which may be heard by one or more parties to the call, muting the microphone of the local telephone and recording the date and time of the remote party's attempt to initiate the three-way call.
Other systems are known which incorporate methods of monitoring calls in telecommunications management systems. For example, the methods include means for detecting tones commonly associated with call bridging and call forwarding attempts. One such method is directed to the detection of tones such as ring signals, busy signals, special information tones (“SIT tones”), dual tone multi-frequency tones (“DTMF”), call progress tones or other similar tones characteristic of the placement of a telephone call.
Yet another known system incorporates spread spectrum techniques to detect three-way calls. The system measures delay times associated with multiple echoes of a reference signal transmitted over a two-way call. This initial echo characteristic is measured and recorded in an initial echo profile. Whether a three-way calling event has occurred is determined by virtue of changes in the delay times and number of echoes in each subsequent echo profile when compared with the initial echo profile. In view of the foregoing, a need clearly exists for a method and system of three-way call detection capable of accurately detecting three-way call attempts in analog and digital telecommunications systems. This method and system may be used in conjunction with any current system, but is preferably implemented within a system that detects three-way call attempts by analyzing the communications path between the originator and recipient in a telecommunications network.